dividing line
noun
1- the boundary between two areas（两个区域间的）分界线：
the dividing line between eastern and western zones.
东区和西区间的分界线。
1.1
- a distinction or set of distinctions marking the difference between two things that are or seem to be closely related密切相关事物间的区别：
the dividing line between what is and what is not permissible is often difficult to draw.
允许和不允许做的事情间的区别往往是难以界定的。